台湾海峡西南部的海陆联合深地震探测资料特点与处理对策*

为调查长乐—南澳断裂带和滨海断裂带的展布、形态和深部构造背景, 福建省地震局使用大容量气枪震源和海底地震仪将深地震探测拓展到台湾海峡西南部, 配合陆上的水库气枪震源、吨级爆破点和流动地震仪实现了海陆双向激发接收。文章详细介绍了2013—2015年间在台湾海峡西南部采集的6条二维广角地震剖面的观测系统、采集参数和数据预处理方法。对资料的整理分析表明: 震源激发参数和仪器接收点位选择合理, 大部分共接收点道集记录能清晰地识别出Pg、PmP、Pn、Sg、SmS等震相; 通过气枪固定点多次激发进行叠加的方法, 获得了信噪比相当于吨级爆破的共炮点道集记录。陆上台站数据品质较佳, 而海底地震仪数据信噪比较低, 可能是由于海底吸收衰减较为严重。数据处理中针对台湾海峡西南部沉积层速度较低且基底面起伏剧烈的问题, 将共接收点域拾取的走时分选到炮域, 避免了表层改正残差造成深部构造假象的问题。

Features of the onshore-offshore seismic data in Southwest Taiwan Strait and some countermeasures for data processing

In order to study the trend, shape and tectonic setting of the Changle—Nan’ao fault and Binhai (littoral) fault, the Earthquake Administration of Fujian Province expanded seismic sounding into the southwest Taiwan Strait using large volume air-gun arrays and Ocean Bottom Seismometers (OBSs), which formed a relatively complete observation system in conjunction with onshore explosions and portable seismometers. In this paper, we introduce in detail the six profiles collected between 2013 and 2015, including the observation system, acquisition parameters, and data preprocessing. Due to rational choice of shooting parameters and receiver position, a variety of seismic phases, including Pg, PmP, Pn, Sg, and SmS, can be clearly identified in most common receiver gathers of the portable seismometers and OBSs. By multiple shooting the air-gun array at fixed site, we obtained several stacked common shot gathers, of which the signal-to-noise ratios were as high as those acquisition with ton-level explosions. Compared with the data recorded by onshore seismometers, the data recorded by OBSs have a relative low signal-to-noise ratio, which probably means that the seabed in this area has a higher absorption. In light of low velocity and acute variety of deposition thickness in the southwest Taiwan Strait, we transfer the travel times, which were picked up on the common receiver gathers to shot domain, in order to avoid the errors of sediment model, which resulted in pseudo deep structures.